Shock absorber

ABSTRACT

A shock absorber for a starter is presented. The shock absorber includes a rotary disk, a stationary disk and a disk spring. The rotary disk is pressed by the disk spring against a stationary disk to generate frictional force when the rotary disk is rotated by an excessive shock thereby absorbing the shock. The rotary disk has a plurality of press-formed rectangular dimples at a surface opposite the stationary disk, and each side of each the rectangular dimple inclines to a direction of rolling of the raw material of the rotary disk.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority from JapanesePatent Applications: Hei 11-300442, filed Oct. 22, 1999, Hei 11-300480,filed Oct. 22, 1999, Hei 11-300492, filed Oct. 22, 1999, and 2000-45589,filed Feb. 23, 2000, the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a shock absorber for absorbing a shock.

2. Description of the Related Art

JP-A-63-277859 discloses a starter equipped with a shock absorber forinterrupting transmission of an excessive torque. In such a shockabsorber for a starter, a rotary disk is pressed against a stationarydisk to generate a frictional force so that rotation of the rotary diskcan be controlled. Accordingly, when a shock that is more than a certainnormal torque is applied to the rotary disk, the rotary disk slips orrotates, thereby absorbing the shock.

Such a rotary disk has a plurality of dimples and small banks formedaround the dimples at a height of about tens of microns, providing apress-formed frictional surface. An amount of grease is filled in thespaces (dimples) between the stationary disk and the rotary disk withthe banks being in contact with the surface of the stationary disk toprevent seizing.

Because an array direction of the dimples is the same as the directionof the rolling of the raw material of the rotary disk, the height of thebanks are not formed even. That is, the bank of the sides in parallelwith the direction of rolling is lower than the bank of the sides thatis perpendicular to the direction of rolling. Only two sides of therectangular dimples can touch the stationary disk. Therefore, the twoside-banks may be worn away more easily than the four side-banks. Thislowers the lifetime of the shock absorber.

If another two-side banks start touching the stationary disk after thefirst two side-banks initially touched the stationary disk have wornaway, the friction factor changes too abruptly to control thetransmission torque.

As the rotary disk has rotated for a long time, the spaces for thegrease between the head of the dimple and the bottom thereof becomenarrower. Accordingly, a sufficient amount of grease can not be suppliedto the sliding surfaces of the disks. This causes the seizing andshortens the lifetime.

SUMMARY OF THE INVENTION

The invention has been made in view of the above problem and has anobject of providing a shock absorber that can make the height of thebanks (or raised portions) of the rectangular dimples even.

According to a main feature of the invention, rotary disk of a shockabsorber has a plurality of press-formed rectangular dimples at asurface opposite the stationary disk. The rectangular dimples have foursides that incline to a direction of rolling of the raw material of therotary disk. In such a case, the difference in height between the fourside banks can be effectively reduced so that four banks can touch thestationary disk evenly.

Preferably, each the rectangular dimples may be square dimples. In sucha case, each side of the square shape inclines to the direction ofrolling at 45 degree in angle.

The plurality of rectangular dimples can be formed on the surface of thestationary disk instead of the rotary disk.

According to another feature of the invention, a rotary disk of theshock absorber has an oil hole or an oil groove as an oil reservoir. Theoil hole or oil groove penetrates the rotary disk in the thicknessdirection.

Even if the surface of the rotary disk wears away to some extent, theoil hole or oil groove does not disappear, so that grease can beprevented from reducing. The grease filled in the oil hole or oil grooveis supplied to the sliding surfaces as long as the rotary disk rotates,so that the seizing can be prevented.

Preferably, the rotary disk has a plurality of oil holes atcircumferentially and radially different positions, and the plurality ofoil holes are disposed so that the radial positions thereof partiallyoverlap each other on a circumference of the rotary disk. When therotary disk rotates, a plurality of rotation loci of the oil holes isformed to partly overlap each other.

Accordingly, the supply of the grease is not stopped in the radialdirection of the rotary disk where the plurality of the oil holes areformed, so that the grease can be continuously and uniformly supplied tothe friction surface of the rotary disk.

The plurality of oil holes is preferably disposed spiral about thecenter of the rotary disk over the circumference of the rotary disk. Theplurality of oil holes is dispersed evenly in the circumferential andradial directions so that the flatness of the rotary disk's surfaceopposite the stationary disk can be secured. This prevents unevencontacts with the stationary disk.

The rotary disk can have a first one of the oil holes that opensradially outward and a second one of the oil holes that opens radiallyinward, and the first one and the second one of the oil holes extend topartially overlap each other in the radial direction. Accordingly, thefirst one and the second one of the oil holes partially overlap eachother when the rotary disk rotates. Therefore, the grease can besupplied evenly to the friction surface of the rotary disk.

In addition, the rigidity of the rotary disk becomes smaller than theoil holes not open to either outward or inward, so that the rotary diskcan deform along the stationary disk. This equalizes the pressure on thesurface of the rotary disk to result in even frictional wear, so thatthe lifetime of the rotary disk can be increased.

The first one and second one of the oil holes preferably incline to therotational direction from radial directions, so that the grease canenter the first and the second ones of the oil holes while the rotarydisk rotates. In other words, the grease can be continuously supplied tothe friction surface of the rotary disk.

The stationary disk of the shock absorber can have oil reservoirsinstead of the rotary disk.

In this case, the same effect as the rotary disk having the oilreservoir can be obtained. Therefore, reduction in strength of therotary disk can be avoided.

According to another feature of the invention, a rotary disk of a shockabsorber is comprised of a plurality of circumferentially dividedpieces.

Because the surface area of each the divided piece is small relative tothe entire surface area of the rotary disk, each divided piece can havea high flatness. As a result, pressure can be applied to each dividedpiece evenly, so that the surface pressure of the rotary disk can bemade even.

A stationary disk can have a plurality of circumferentially dividedpieces, instead of the rotary disk.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and characteristics of the present invention aswell as the functions of related parts of the present invention willbecome clear from a study of the following detailed description, theappended claims and the drawings. In the drawings:

FIG. 1 is a half cross-sectional longitudinal view of a starter;

FIG. 2 is an enlarged fragmentary cross-sectional view illustrating amain portion of a speed reduction unit and a shock absorber according toa first embodiment of the invention;

FIG. 3A is a cross-sectional side view of a rotary disk of the shockabsorber according to the first embodiment, and FIG. 3B is a plan viewof the same;

FIG. 4A is a plan view illustrating an array of dimples and projectionsformed on the rotary disk or stationary disk and FIG. 4B is across-sectional view of the same cut along line IVB—IVB;

FIG. 5A is a cross-sectional side view of a rotary disk of the shockabsorber according to a second embodiment of the invention, and FIG. 5Bis a plan view of the same;

FIG. 6 is a plan view of a rotary disk of a shock absorber according toa third embodiment of the invention;

FIG. 7 is a fragmentary enlarged cross-sectional view of a main portionof a shock absorber according to a fourth embodiment of the invention;

FIG. 8A is a cross-sectional side view of a rotary disk of a shockabsorber according to a fifth embodiment of the invention, and FIG. 8Bis a plan view of the same;

FIG. 9A is a cross-sectional side view of a rotary disk of a shockabsorber according to a sixth embodiment of the invention, and FIG. 9Bis a plan view of the same;

FIG. 10 is a plan view of a rotary disk of a shock absorber according toa seventh embodiment of the invention; and

FIG. 11 is a plan view illustrating a method of manufacturing dividedpieces that form the rotary disk of the shock absorber according to theseventh embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

Shock absorber according to a first embodiment of the invention that ismounted into a starter is described with reference to FIGS. 1-4.

As shown in FIG. 1, starter 1 includes a speed reduction unit, outputshaft 2 and a shock absorber according to a first embodiment of theinvention. The speed reduction unit reduces the rotation speed of laterdescribed starter motor and transmits it to output shaft 2. The shockabsorber absorbs an excessive torque or a shock applied to the speedreduction unit.

The starter motor is a well-known DC motor that is comprised of armature3, stator poles 4, yoke 5 and brushes 6. When a key switch is turned onand a pair of internal contacts of magnet switch 7 is closed, armature 3is energized through brushes 6 to rotate.

Magnet switch 7 opens or closes the internal contacts as a plunger (notshown) moves to drive pinion gear 9, together with one-way clutch 10,back and forth.

Pinion gear 9 is slidably fitted to the outer periphery of output shaft2 via bearing 11. Pinion gear 9 is driven forward (to the left inFIG. 1) together with one-way clutch 10 by lever 8 to engage engine ringgear 12 to transmit the torque to ring gear 12.

One way clutch 10 is fitted to the outer periphery of output shaft 2 viaa helical spline to transmit the rotation of output shaft 2 to piniongear 9 and to interrupt transmission of torque between output shaft 2and pinion gear 9.

The speed reduction unit is comprised of sun gear 13, ring-shapedinternal gear 14 having internal teeth at portions around sun gear 13,and planetary gears 14 disposed between sun gear 13 and internal gear 14to mesh the same. Sun gear 13 has external teeth formed around the outerperiphery of armature shaft 3 a. The speed reduction unit and the shockabsorber are covered by center case 16, which is described below.

Internal gear 14 is provided with cylindrical outer wall 14 a, which isrotatably fitted into the inner periphery of outer cylindrical portion16 c of center case 16. Internal gear 14 is connected with rotary disk20 at an axial end of outer wall 14 a and is restricted to rotate asrotary disk 20 is at a standstill. A plurality of recesses 14 b isformed at the inner periphery of the axial end of outer wall 14 a atequal intervals.

Planetary gear 15 meshes sun gear 13 and internal gear 14, and isrotatably supported by pin 17 force-fitted to a rear portion of outputshaft 2 via bearing 18.

When sun gear 13 is rotated by armature 3, planetary gear 15 rotates onits axis and revolves around sun gear 13. Thus, revolution of planetarygear 15 is transmitted through pin 17 to output shaft 2 to rotate outputshaft 2.

Center piece 16 has annular front wall 16 a disposed perpendicularly tooutput shaft 2, inner cylindrical portion 16 b extending axiallyrearward from the inner peripheral edge of front wall 16 a, and outercylindrical portion 16 c extending from the outer peripheral edge offront wall 16 a. The rear edge of outer cylindrical portion 16 c isconnected with the front edge of yoke 5, and the inner periphery ofinner cylindrical portion 16 b rotatably supports output shaft 2 viabearing 19. Male screw 16 d is formed on the outer periphery of innercylindrical portion 16 b.

Shock absorber is comprised of rotary disk 20, stationary disk 21, discspring 22, and adjust screw 23.

As shown in FIGS. 3A and 3B, rotary disk 20 is a press-formed metalring. Rotary disk 20 is disposed in contact with front wall 16 a and isdetained in internal gear 14 by a plurality of claws 20 a, which areformed at the circumference of outer wall 14 a, respectively insertedinto the plurality of recesses 14 b.

As shown in FIG. 4B, a plurality of projections or banks 24 is formed atopposite surface of rotary disk 20. Banks 24 are formed when a pluralityof dimples 25 (depressions) are press-formed at the surfaces of rotarydisk 20. The projections or banks are arranged in a rectangularconfiguration.

Square dimples 25 are formed by square-pole punches (not shown), andfour sides of the square dimples respectively incline 45 degree in angleto a direction of rolling of the raw material of rotary disk 20.

Stationary disk 21 is also a press-formed metal ring similar to rotarydisk 20, and is disposed in contact with the frictional surface ofrotary disk 20. Stationary disk 21 has a plurality of circumferentiallydisposed openings 21 a. A plurality of projections 16 e is formed atfront wall 16 a and respectively. inserted into openings 21 a so thatthe rotation of stationary disk 21 can be stopped by center case 16.

Disc spring 22 is a common spring for pushing stationary disk 21 towardrotary disk 20.

Adjust screw 23 engages male screw 16 d of inner cylindrical portion 16b of center case 16 to adjust an initial load of disc spring 22according to the screw-in distance thereof.

Operation of starter 1 will be described hereafter.

When a coil (not shown) of magnet switch 7 is energized by turning on akey switch, plunger is pulled right in FIG. 1 to move pinion gear 9forward, together with one-way clutch 10, along output shaft 2.

When the plunger moves and the internal switch of magnet switch 7closes, armature 3 is energized to rotate. The rotation speed ofarmature 3 is reduced by the speed reduction unit and transmitted tooutput shaft 2.

The rotation of output shaft 2 is transmitted to pinion gear 9 throughone-way clutch 10. When pinion gear moves to a position to engage ringgear 12, the rotation of pinion gear is transmitted to ring gear 12,which starts the engine.

After engine starts, the key switch is turned off to deenergize thecoil, the plunger returns to the initial position, so that pinion gear 9separates from ring gear 12 and goes back along output shaft 2. Then,the internal switch of magnet switch 7 opens to cut electric supply toarmature 3 to stop the same.

Operation of the shock absorber is described next.

If a shock that is larger than a certain torque is applied to rotarydisk 20 of the shock absorber, rotational disk 20, which has been at astand still, rotates to absorb the shock. In other words, if the shockis caused when pinion gear 9 engages ring gear 12, the shock istransmitted through output shaft 2 and internal gear 14 to rotary disk20. Then, rotary disk 20 slides in the rotational direction relative tofront wall 16 a of center case 16 and stationary disk so that internalgear 14, which is restricted by rotary disk 20, can rotate. Accordingly,a shock larger than a certain torque is prevented from being applied tothe torque transmission system between armature 3 and pinion gear 9.

None of the four sides of square dimples is parallel with the directionof roll, and each side equally inclines to the direction. Accordingly,all banks 24 formed along the sides of the square shapes can be madeeven in height.

As a result, banks 24 of each dimple 25 engage stationary disk 21.Therefore, the wear rate of banks 24 can be made smaller than the priorart case in which only two banks 24 engage stationary disk 21. Thisincreases the lifetime of the shock absorber. Because four banks 24evenly engage stationary disk 21 from the beginning, the frictionalfactor may not change abruptly during the operation. This makes torquecontrol easy.

Variation of the First Embodiment

Dimples 25 can be formed on stationary disk 21 such as shown in FIGS. 4Aand 4B.

Corners of each dimple may be either sharp or round.

The shock absorber according to the invention can be applied to a driveunit other than the starter, such as a brake or a clutch.

Second Embodiment

A shock absorber according to a second embodiment of the invention willbe described with reference to FIGS. 5A and 5B.

Rotary disk 20 is a press-formed metal ring. Rotary disk 20 is disposedin contact with front wall 16 a and is detained in internal gear 14 by aplurality of claws 20 a, which are formed at the circumference of outerwall 14 a, respectively inserted into the plurality of recesses 14 b.

A plurality of projections or banks (not shown) is formed at oppositesurfaces of rotary disk 20 in the same manner as described withreference to FIGS. 3A and 3B. Banks 24 are formed when a plurality ofdimples 25 (depressions/not shown) is press-formed at the surfaces ofrotary disk 20.

In addition, rotary disk 20 has a plurality of oil holes 24 penetratingthe same in the thickness direction. The plurality of oil holes 24 isdisposed almost evenly in the circumferential direction. Each group offour circumferentially lined oil holes 24 forms a spiral line about thecenter O of rotary disk 20 thereof so that the radial position thereofoverlaps one another.

More in detail, in FIG. 5B, four spirally lined oil holes 24 arerespectively named, from inside to the outside, first oil hole 24 a,second oil hole 24 b, third oil hole 24 c and fourth oil hole 24 d. Ifrotary disk 20 rotates, first oil hole 24 a and second oil hole 24 bpartially overlap each other on a circumference of rotary disk 20.Second oil hole 24 b and third oil hole 24 c also partially overlap eachother, and third oil hole 24 c and fourth oil hole 24 d partiallyoverlap each other, on circumferences of rotary disk 20.

Four spirally lined oil holes 24 form oil hole group 24A. A plurality ofoil hole groups 24A is disposed in succession all around rotary disk 20.That is, first oil hole 24 a of one group 24A overlaps in the radialdirection with (or can be located with the same circumferential positionas) fourth oil hole 24 d of another group 24 adjacent thereto. However,first oil hole 24 a of one group 24A and fourth oil hole 24 d of anothergroup 24A, as shown in FIG. 5B, are preferably located at the samecircumferential position of rotary disk 20 as one of the plurality ofclaws 20 a.

When rotary disk 20 is assembled, grease is applied to the frictionsurface and to the plurality of oil holes 24.

Stationary disk 21 is also a press-formed metal ring similar to rotarydisk 20, and is disposed in contact with the frictional surface ofrotary disk 20. As described in the first embodiment with reference toFIG. 2, stationary disk 21 also has a plurality of circumferentiallydisposed openings 21 a. A plurality of projections 16 e is formed atfront wall 16 a and is respectively inserted into openings 21 a so thatthe rotation of stationary disk 21 can be stopped by center case 16.

Disc spring 22 is a common spring for pushing stationary disk 21 towardrotary disk 20. Adjust screw 23 engages male screw 16 d of innercylindrical portion 16 b of center case 16 to adjust an initial load ofdisc spring 22 according to a screw-in distance thereof.

Even if the friction surface (projections) of rotary disk 20 so wearsaway that the grease on the surface decreases, the plurality of oilholes would not disappear. Accordingly, the grease filled in theplurality of oil holes 24 is supplied to the friction surface as long asrotary disk 20 rotates. This prevents seizing of rotary disk 20.

When rotary disk 20 slides to rotate, a plurality of loci of oil holes24 is formed in the radial direction of rotary disk 20 (four in thisembodiment). Because the plurality of loci partly overlaps one another,the supply of the grease from the range between first oil hole 24 a andfourth oil hole 24 d may not be intermitted in the radial direction ofrotary disk 20. As a result, the grease can be supplied to the frictionsurface of rotary disk 20 evenly, so that an excellent slip torque canbe obtained. In particular, a plurality of oil hole group 24A is formedspiral about the center O of rotary disk 20. This can supply the greaseall around the friction surface of rotary disk 20 with a minimum numberof oil holes.

Flatness of rotary disk 20 can be also assured so that incompletecontact of rotary disk 20 with front wall 16 a of center case 16 andstationary disk 21 can be prevented.

Moreover, first oil hole 24 a of one group and fourth oil hole 24 d ofanother group can be located where claws 20 a are located. This preventsthe rigidity of rotary disk 20 from lowering.

Third Embodiment

Rotary disk 20 of a shock absorber according to a third embodiment ofthe invention is described with reference to FIG. 6.

Oil holes at the inner peripheral edge (or the outer peripheral edge) ofrotary disk 20 can open inward. In this case, the same effect as thesecond embodiment can be obtained.

Fourth Embodiment

Shock absorber according to a fourth embodiment of the invention isdescribed with reference to FIG. 7.

Oil recesses or reservoirs 25 and 26 are formed on the surface of centercase 16 and on the surface of stationary disk 21 opposite the frictionsurfaces of rotary disk 20. If a through hole for oil recess 25 isformed at wall 16 a to penetrate the same in the thickness direction,grease may leak out of center case. A recess is also formed for oilreservoir 26 at stationary disk 21. Oil recesses 25 and 26 arepreferably formed at the same positions as oil holes 24, which areradially and circumferentially different from each other but overlapeach other.

Accordingly, the same effect as oil hole 24 formed at rotary disk 20 canbe obtained. If oil recesses 25, 26 are formed at front wall 16 a andstationary disk 21, the number of oil holes 24 of rotary disk 20 can bereduced or eliminated.

As a result, oil holes 24 prevent rotary disk 20 from reducing thestrength thereof.

Fifth Embodiment

A rotary disk of a shock absorber according to a fifth embodiment isdescribed with reference to FIGS. 8A and 8B.

Rotary disk 20 is provided with oil grooves 27. Each oil groove 27 isformed to penetrate rotary disk 20 in the thickness direction and toextend long and narrowly in the radial direction to hold grease as oilhole 24.

Oil grooves 27 are formed of a plurality of first oil grooves 27 a whichopens radially outward and a plurality of second oil grooves 27 b whichopens radially inward. Oil grooves 27 a and 27 b are alternatelydisposed in the circumferential direction. Each first oil groove 27 aand each second oil groove 27 b overlap each other at the bottom portionthereof in the radial direction if they are put side by side in thecircumferential direction. In other words, the radially inner headportion of first oil grooves 27 a is formed to extend beyond thecenterline of the width of rotary disk 20 (one-dot chain line in FIG.8B). On the other hand, the radially outer bottom portion of second oilgrooves 27 b is formed to extend beyond the centerline.

When rotary disk 20 rotates, the rotating locus of first oil groove 27 aand the rotating locus of second oil groove 27 b overlap each other.Therefore, the grease can be continuously supplied to the frictionsurface in the width direction of rotary disk 20. First oil groove 27 aopens outward at the outer periphery of rotary disk 20, and second oilgroove 27 b opens inward at the inner periphery of rotary disk.Therefore, rotary disk 20 becomes flexible so that rotary disk 20 caneasily deform along stationary disk. As a result, the surface pressureof rotary disk 20 becomes more uniform, and the friction surface canwear away uniformly. This increases the lifetime of rotary disk.

Sixth Embodiment

A shock absorber according to a sixth embodiment of the invention isdescribed with reference to FIGS. 9A and 9B.

Oil grooves 27 (first oil grooves 27 a and second oil grooves 27 b) areformed at rotary disk 20. First oil grooves 27 a and second oil grooves27 b incline to the rotation direction of rotary disk 20.

When rotary disk 20 rotates, the grease filled at the outer periphery ofrotary disk 20 enters the inside of first oil grooves 27 a from theopening of first oil grooves 27 a. In the same manner, the grease filledat the inner periphery of rotary disk 20 enters the inside of second oilgrooves 27 b from the opening of second oil grooves 27 b. In otherwords, it is possible to intentionally take the outside grease intofirst and second oil grooves 27 a and 27 b. Therefore, grease is alwaysfilled in first and second oil grooves 27 a and 27 b to be continuouslysupplied to the friction surface of rotary disk 20, so that a reliableshock absorber can be provided.

Seventh Embodiment

A shock absorber according to a seventh embodiment is described withreference to FIGS. 10 and 11.

A plurality of projections or banks (not shown) is formed at oppositesurfaces of rotary disk 20. The plurality of banks is formed when aplurality of dimples is press-formed at the surfaces of rotary disk 20.

Rotary disk 20 is formed of a plurality of divided pieces 20A, as shownin FIG. 10. Because the plurality of divided pieces 20A is stamped outfrom portions of metal plate 24 close to each other, as shown in FIG.11, each divided piece 20A can have a high flatness, so that the yieldrate of the raw material is high. In addition, because each dividedpiece 20A is disposed in a circle at small intervals, it is possible tofill grease in gaps between divided pieces 20A. In order to prevent eachdivided piece 20A from moving to the inner periphery thereby to removethe gaps, center case 16 is provided with a circular support forsupporting the inner periphery of rotary disk 20.

Moreover, the spring force of disk spring 22 can be evenly applied toeach divided piece 20A, so that the surface pressure of rotary disk 20can be made even. In other words, partial contact of rotary disk withfront wall 16 a and stationary disk 21 can be prevented. This reduceswear of the friction surface and increases the lifetime of the shockabsorber.

Variations

Instead of rotary disk 20, stationary disk 21 can also divided in thecircumferential direction. Each of the shock absorbers according to theabove embodiments can be applied to any driving device other than astarter, such as a brake or a clutch.

In the foregoing description of the present invention, the invention hasbeen disclosed with reference to specific embodiments thereof. It will,however, be evident that various modifications and changes may be madeto the specific embodiments of the present invention without departingfrom the broader spirit and scope of the invention as set forth in theappended claims. Accordingly, the description of the present inventionis to be regarded in an illustrative, rather than restrictive, sense.

What is claimed is:
 1. A shock absorber comprising a rotary disk, astationary disk and a disk spring, said rotary disk being pressed bysaid disk spring against said stationary disk to generate frictionalforce when said rotary disk is rotated relative to said stationary diskby an excessive shock thereby absorbing the shock, said rotary diskbeing formed from a rolled material that is rolled in a direction ofrolling; said rotary disk having a plurality of rectangular dimples andprojections on an axially outwardly facing surface of said rotary diskto confront said stationary disk, each of said projections extendingoutwardly from all sides of one of said rectangular dimples to form arectangular configuration, wherein each side of each of said projectionsis equally angled relative to said direction of rolling.
 2. The shockabsorber as claimed in claim 1, wherein each of said projections isarranged in a square configuration and each side of each of said squareprojections is angled relative to the direction of rolling at 45degrees.
 3. A shock absorber comprising a rotary disk, a stationary diskand a disk spring, said rotary disk being pressed by said disk springagainst said stationary disk to generate frictional force when saidrotary disk is rotated relative to said stationary disk by an excessiveshock thereby absorbing the shock, said stationary disk being formedfrom a rolled material being rolled in a direction of rolling; saidstationary disk having a plurality of rectangular dimples andprojections, each of said projections extending outwardly from anaxially outwardly facing surface of said stationary disk around each ofsaid rectangular dimples and confronting said rotary disk, each of saidprojections having sides being equally inclined relative to saiddirection of rolling.
 4. The shock absorber as claimed in claim 3,wherein each of said projections is arranged in a square configurationand each side of each of said square projections is angled relative tothe direction of rolling at 45 degrees.
 5. An engine starter including apinion gear, a speed reduction unit and a shock absorber disposedbetween said pinion gear and said speed reduction unit, said shockabsorber comprising a stationary disk, a spring, and a rotary diskpressed against said stationary disk to generate frictional force whensaid rotary disk is rotated by an excessive shock thereby absorbing theshock, said rotary disk being formed from a rolled material that isrolled in a direction of rolling, said rotary disk having a plurality ofrectangular dimples and projections, each of said projections extendingoutwardly from an axially outwardly facing surface of said rotary diskaround each of said dimples and confronting said stationary disk, eachof said projections being equally inclined relative to the direction ofrolling of the rolled material.
 6. An engine starter including a piniongear, a speed reduction unit and a shock absorber disposed between saidpinion gear and said speed reduction unit, said shock absorbercomprising a stationary disk, a spring, and a rotary disk pressedagainst said stationary disk to generate frictional force when saidrotary disk is rotated relative to said stationary disk by an excessiveshock thereby absorbing the shock, at least one of said stationary androtary disks being formed from a rolled material being rolled in adirection of rolling and having a plurality of press-formed rectangulardimples and projections formed within an axially outwardly facingsurface of said at least one of said stationary and rotary disks andconfronting another of the at least one stationary and rotary disks,wherein each side of each of said rectangular dimples is equally angledrelative to said direction of rolling.
 7. A method of forming a frictiondisk for a shock absorber of a starter motor, the method comprising:rolling a raw material into a plate, thereby aligning an internalstructure of the raw material in a direction of the rolling; stamping asubstantially circular body from the plate; and pressing a plurality ofrectangular dimples into an axially outwardly facing surface of thecircular body, thereby causing a plurality of projections to rise fromthe surface of the substantially circular body adjacent edges of thedimples, wherein each side of the rectangular dimples and theprojections is equally aligned at an angle relative to the rollingdirection of the raw material.
 8. The method according to claim 7,wherein each of the rectangular dimples and projections are aligned atabout 45 degrees relative to the rolling direction of the raw material.9. The method according to claim 7, wherein the raw material is steel.10. The method according to claim 7, wherein the friction disk is arotary disk.
 11. The method according to claim 7, wherein the frictiondisk is a stationary disk.
 12. The method according to claim 7, furthercomprising forming radially outwardly extending tab portions annularlyspaced about an outer periphery of the substantially circular body. 13.The method according to claim 12, further comprising bending theradially outwardly extending tab portions in an axial direction.
 14. Themethod according to claim 12, wherein the axial direction of the benttab portions corresponds to the axially facing direction of theprojection.